OK,
looks like the windows sharing service has failed. to check go into
Start (OK, it doesn't say start anymore but you know what I mean!
)
Run
eventvwr
then look at the system and application logs to look for mention of the network services (pay particular attention o any red X messages.)
You could also check what the settings in control panel, admin tools, services are with respect to networking and file sharing.
Most proabbly windows has done an auto update alongside your iTunes one. Teh one thing Vista brought in is the extra security around programs making admin changes so its highly unlikely that iTunes did anything in this